Siemens SIMATIC NET CP 243-1 IT Technical Manual page 20

Features and Functions
Data communication via Industrial Ethernet
Data communication via the CP 243-1 IT is based on Ethernet and is thus not de-
terministic (i.e., specific response times are not guaranteed). 10 and 100-Mbit net-
works are supported in full and half-duplex.
In addition, the CP 243-1 IT supports the auto-negotiation function for automatically
negotiating the operating mode and the transmission speed to be used. The mode
and the transmission speed can also be permanently specified by the user when
configuring the CP 243-1 IT. If the CP 243-1 IT doesn't have a valid configuration, it
always uses "auto-negotiation" mode.
Note
Auto-negotiation mode only works when all connected network components sup-
port this mode.
Industrial Ethernet and TCP/IP do not allow time-deterministic data flow. There is
no way to know when a geographically remote CPU will execute the requested
jobs. The responses of the geographically removed CPU are asynchronous to the
CPU cycle of the local S7-200 CPU. This is why TCP/IP-based communication is
only partly suitable for use in widespread applications with time requirements (e.g.,
control circuits, cyclic precisely timed scanning).
20
03/03
CP 243-1 IT
J31069-D0429-U001-A0-7618